Comparison of the Accuracy of Different Transfer Impression Techniques for Osseointegrated Implants.

The aim of this study was to evaluate 3 transfer techniques used to obtain working casts of implant-supported prostheses through the marginal misfit and strain induced to metallic framework. Thirty working casts were obtained from a metallic master cast, each one containing 2 implant analogs simulating a clinical situation of 3-unit implant-supported fixed prostheses according to the following transfer impression techniques: group A, squared transfers splinted with dental floss and acrylic resin, sectioned, and re-splinted; group B, squared transfers splinted with dental floss and bis-acrylic resin; and group N, squared transfers not splinted. A metallic framework was made for marginal misfit and strain measurements from the metallic master cast. The misfit between the metallic framework and working casts was evaluated with an optical microscope following the single-screw test protocol. In the same conditions, the strain was evaluated using strain gauges placed on the metallic framework. The data were submitted to one-way analysis of variance followed by the Tukey test (α = 5%). For both marginal misfit and strain, there were statistically significant differences between groups A and N (P < .01) and groups B and N (P < .01), with greater values for group N. According to the Pearson test, there was a positive correlation between the misfit and strain variables (r = 0.5642). The results of this study showed that the impression techniques with splinted transfers promoted better accuracy than the nonsplinted technique, regardless of the splinting material used.

Effects of horizontal misfit and bar framework material on the stress distribution of an overdenture-retaining bar system: a 3D finite element analysis.

PURPOSE: To evaluate the influence of horizontal misfit change and bar framework material on the distribution of static stresses in an overdenture-retaining bar system using finite element (FE) analysis. MATERIALS AND METHODS: A 3D FE model was created including two titanium implants and a bar framework placed in the anterior part of a severely resorbed jaw. The model set was exported to mechanical simulation software, where horizontal displacement (10, 50, 100, and 200 µm) was applied simulating the settling of the framework, which suffered shrinkage during laboratory procedures. Four bar materials (gold alloy, silver-palladium alloy, commercially pure titanium, and cobalt-chromium alloy) were also simulated in the analysis using 50 µm as the horizontal misfit. Data were qualitatively evaluated using von Mises stress, given by the software. RESULTS: The misfit amplification presented a great increase in the stress levels in the inferior region of the bar, screw-retaining neck, cervical and medium third of the implant, and cortical bone tissue surrounding the implant. The higher stiffness of the bar presented a considerable increase in the stress levels in the bar framework only. CONCLUSION: The levels of static stresses seem to be closely linked with horizontal misfit, such that its amplification caused increased levels of stress in the structures of the overdenture-retaining bar system. On the other hand, the stiffness of the bar framework presented a lower effect on the static stress levels.

Evaluation of stress distribution in overdenture-retaining bar with different levels of vertical misfit.

PURPOSE: To evaluate the effects of different levels of vertical misfit between implant and bar framework on distribution of static stresses in an overdenture-retaining bar system using finite element analysis. MATERIAL AND METHODS: A 3D finite element model (11,718 elements and 21,625 nodes) was created and included two titanium implants and a bar framework placed in the medial region of the anterior part of a severely reabsorbed-jaw. All materials were presumed to be linear elastic, homogenous, and isotropic. Mechanical simulation software (NEiNastran 9.0) was used, where displacements were applied on the end of the bar framework to simulate the closure of the vertical misfits (5, 25, 50, 100, 200, and 300 µm) after tightening of the screws. Data were qualitatively evaluated using Von Mises stress given by the software. RESULTS: The models showed stress concentration in cortical bone, corresponding to the cervical part of the implant, and in cancellous bone, corresponding to the apical part of the implant; however, in these regions few changes were observed in stress to the misfits studied. While in the bar framework, retaining-screw neck, and implant platform, a considerable stress increase proportional to the misfit amplification was observed. CONCLUSIONS: The different levels of vertical misfit did not considerably influence the static stress levels in the peri-implant bone tissue; however, the mechanical components of the overdenture-retaining bar system are more sensitive to lack of passive fit.

Influence of material of overdenture-retaining bar with vertical misfit on three-dimensional stress distribution.

PURPOSE: This study evaluated the effects of different bar materials on stress distribution in an overdenture-retaining bar system with a vertical misfit between implant and bar framework. MATERIALS AND METHODS: A three-dimentional finite element model was created including two titanium implants and a bar framework placed in the anterior part of a severely reabsorbed jaw. The model set was exported to mechanical simulation software, where displacement was applied to simulate the screw torque limited by 100-microm vertical misfit. Four bar materials (gold alloy, silver-palladium alloy, commercially pure titanium, cobalt-chromium alloy) were simulated in the analysis. Data were qualitatively evaluated using Von Mises stress given by the software. RESULTS: The models showed stress concentration in cortical bone corresponding to the cervical part of the implant, and in cancellous bone corresponding to the apical part of the implant; however, in these regions few changes were observed in the levels of stress on the different bar materials analyzed. In the bar framework, screw, and implant, considerable increase in stress was observed when the elastic modulus of the bar material was increased. CONCLUSIONS: The different materials of the overdenture-retaining bar did not present considerable influence on the stress levels in the periimplant bone tissue, while the mechanical components of the system were more sensitive to the material stiffness.